ALBERT

Description: The present study aimed to develop an integrated treatment of agro-industrial waste for biofuel (biogas and syngas) production and for phosphorus recovery. In the first step, an anaerobic digestion (AD) process was carried out on two different mixtures of raw agro-industrial residues. Specifically, a mixture of asparagus and tomato wastes (mixture-1) and a mixture of potatoes and kiwifruit residues (mixture-2) were investigated. The results proved that the properties of mixtures notably affect the evolution of the digestion process. Indeed, despite the lower organic load, the maximum biogas yield, of about 0.44 L/gCODremoved, was obtained for mixture-1. For mixture-2, the digestion process was hindered by the accumulation of acidity due to the lack of alkalinity in respect to the amount of volatile fatty acids. In the second step, the digestates from AD were utilized for syngas production using supercritical water gasification (SCWG) at 450 °C and 250 bar. Both the digestates were rapidly converted into syngas, which was mainly composed of H2, CO2, CH4, and CO. The maximum values of global gasification efficiency, equal to 56.5 g/kgCOD, and gas yield, equal to 1.8 mol/kgTS, were detected for mixture-2. The last step of the integrated treatment aimed to recover the phosphorus content, in the form of MgKPO4ˑ6H2O, from the residual liquid fraction of SCWG. The experimental results proved that at pH = 10 and Mg/P = 1 it is possible to obtain almost complete phosphorus removal. Moreover, by using the scanning electronic microscopy, it was demonstrated that the produced precipitate was effectively composed of magnesium potassium phosphate crystals.

Description: The pollution of water by nitrates represents an important environmental and health issue. The development of sustainable technologies that are able to efficiently remove this contaminant is a key challenge in the field of wastewater treatment. Chemical denitrification by means of zero-valent metallic elements is an interesting method to reduce the oxidized forms of nitrogen. Compared to other metallic reactants, zero-valent magnesium (ZVM) has many profitable aspects, but its use for nitrate removal has scarcely been investigated. In the present work, several batch tests were conducted to examine the concurrent effects of pH, initial nitrate concentration and Mg0 quantity on process performance. The experimental results proved that at pH 3, for a given initial nitrate concentration, the dose of ZVM largely influences process efficiency. In particular, with a ratio between Mg0 and initial N-NO3− amount (Mg/NNi) of 0.33 g/mg, it is possible to obtain complete denitrification within 30 min. Beyond this ratio, no further improvement of treatment was observed. The experiments allowed us to identify the nitrogen forms produced during the treatment. Nitrogen gas was generally the main reaction product, but the trends of the different compounds (NO3−, NO2−, NH4+ and N2) notably changed in response to the modification of operating parameters. Moreover, the results demonstrated that, in a highly acidic environment, when treating solutions with a low nitrate concentration, process performances are unsatisfactory even when using a high Mg/NNi ratio. By increasing the process pH to 5 and 7, a significant denitrification decline occurred. Furthermore, at these pH levels, the enhancement of nitrate concentration caused a progressive process deterioration. Through detailed analysis of experimental results, reactions kinetics and new mathematical equations, able to describe the trends of different nitrogen forms, have been defined. Moreover, reactions pathways have been proposed. Finally, the characterization of exhausted material allowed us to identify the corrosion products formed during the treatment.

Description: Water, Vol. 10, Pages 404: Nanoscopic Zero-Valent Iron Supported on MgO for Lead Removal from Waters Water doi: 10.3390/w10040404 Authors: Alessio Siciliano Carlo Limonti Lead is one of the most toxic heavy metals that can create a severe risk to water ecosystem health. Zero-valent iron is an effective material for Pb2+ removal treatments. In particular, nanoscopic zero-valent iron (nZVI) particles are characterized by high reaction rates; nevertheless, their utilization in water and groundwater remediation techniques requires further investigations. Indeed, it is necessary to define effective methods able to avoid the drawbacks due to the aggregation tendency of nanoparticles and their potential uncontrolled transport in groundwater. In this work, nZVI was supported on magnesium oxide grains (MgO_nZVI) to synthesize an alternative material for lead removal from aqueous solutions. Many experiments were conducted under several operating conditions in order to analyze the effectiveness of the produced material in Pb2+ abatement. The performance of MgO_nZVI was also compared with those detected using commercial microscopic Fe0 (mZVI) as a reactive material. The experimental findings showed a much greater reactivity of the supported nanoscopic iron particles. By means of a kinetic analysis of batch tests results, it was verified that, both for MgO_nZVI and mZVI, the lead abatement follows a pseudo-second-order kinetic law. The reaction rates were affected by the initial pH of the treatment solution and by the ratio between the Fe0 amount and initial lead concentration. The efficiency of MgO_nZVI in a continuous test was steadily around 97.5% for about 1000 exchanged pore volumes (PV) of reactive material, while by using mZVI, the lead removal was approximately 88% for about 600 PV. X-ray diffraction (XRD) and energy-dispersive spectroscopy EDS analyses suggested the formation of typical iron corrosion products and the presence of metallic lead Pb0 and Pb2+ compounds on exhausted materials.

Description: In the Mediterranean region, the disposal of residues of olive oil industries represents an important environmental issue. In recent years, many techniques were proposed to improve the characteristics of these wastes with the aim to use them for methane generation in anaerobic digestion processes. Nevertheless, these techniques, in many cases, result costly as well as difficult to perform. In the present work, a simple and useful process that exploits H2O2 in conjunction with lime is developed to enhance the anaerobic biodegradability of wet olive mill wastes (WMOW). Several tests were performed to investigate the influence of lime amount and H2O2 addition modality. The treatment efficiency was positively affected by the increase of lime dosage and by the sequential addition of hydrogen peroxide. The developed process allows reaching phenols abatements up to 80% and volatile fatty acids productions up to 90% by using H2O2 and Ca(OH)2 amounts of 0.05 gH2O2/gCOD and 35 g/L, respectively. The results of many batch anaerobic digestion tests, carried out by means of laboratory equipment, proved that the biogas production from fresh wet olive mill wastes is hardly achievable. On the contrary, organic matter abatements, around to 78%, and great methane yields, up to 0.34–0.35 LCH4/gCODremoved, were obtained on pretreated wastes.

Description: The composting process of organic fraction of municipal solid waste, besides to the residual compost, generates a wastewater that is characterized by a high organic load. The application of anaerobic processes represents an advantageous solution for the treatment and valorization of this type of wastewater. Nevertheless, few works have been focused on the anaerobic digestion of compost leachate. To overcome this dearth, in the present paper an extensive experimental investigation was carried out to develop and analyse the anaerobic treatment of young leachate in completely stirred tank reactors (CSTR). Initially, it was defined a suitable leachate pretreatment to correct its acidic characteristics that is potentially able to inhibit methanogenic biomass activity. The pretreated leachate was fed to the digester over the start-up phase that was completed in about 40 days. During the operational period, the organic load rate (OLR) changed between 4.25 kgCOD/m3d and 38.5 kgCOD/m3d. The chemical oxygen demand (COD) abatement was higher than 90% for OLR values up to 14.5 kgCOD/m3d and around to 80% for applied loads equal to 24.5 kgCOD/m3d. At this OLR, it was reached the maximum daily biogas production of about 9.3 Lbiogas/(Lreactord). The CH4 fraction was between 70%–78% and the methane production yield in the range 0.34–0.38 LCH4/gCODremoved. The deterioration of biogas production started for OLR values that were over the threshold of 24.5 kgCOD/m3d when a volatile fatty acids (VFA) accumulation occurred and the pH dropped below 6.5. The maximum ratio between VFA and alkalinity (ALK) tolerable in the CSTR was identified to be 0.5 gCH3COOH/gCaCO3. Through an economic analysis, it was proven that the digestion of compost leachate could ensure significant economic profits. Furthermore, the produced digestate had characteristics that were compatible for agricultural applications.

Description: The pollution of water by nitrates represents an important environmental and health issue. The development of sustainable technologies that are able to efficiently remove this contaminant is a key challenge in the field of wastewater treatment. Chemical denitrification by means of zero-valent metallic elements is an interesting method to reduce the oxidized forms of nitrogen. Compared to other metallic reactants, zero-valent magnesium (ZVM) has many profitable aspects, but its use for nitrate removal has scarcely been investigated. In the present work, several batch tests were conducted to examine the concurrent effects of pH, initial nitrate concentration and Mg0 quantity on process performance. The experimental results proved that at pH 3, for a given initial nitrate concentration, the dose of ZVM largely influences process efficiency. In particular, with a ratio between Mg0 and initial N-NO3− amount (Mg/NNi) of 0.33 g/mg, it is possible to obtain complete denitrification within 30 min. Beyond this ratio, no further improvement of treatment was observed. The experiments allowed us to identify the nitrogen forms produced during the treatment. Nitrogen gas was generally the main reaction product, but the trends of the different compounds (NO3−, NO2−, NH4+ and N2) notably changed in response to the modification of operating parameters. Moreover, the results demonstrated that, in a highly acidic environment, when treating solutions with a low nitrate concentration, process performances are unsatisfactory even when using a high Mg/NNi ratio. By increasing the process pH to 5 and 7, a significant denitrification decline occurred. Furthermore, at these pH levels, the enhancement of nitrate concentration caused a progressive process deterioration. Through detailed analysis of experimental results, reactions kinetics and new mathematical equations, able to describe the trends of different nitrogen forms, have been defined. Moreover, reactions pathways have been proposed. Finally, the characterization of exhausted material allowed us to identify the corrosion products formed during the treatment.

Description: The present study aimed to develop an integrated treatment of agro-industrial waste for biofuel (biogas and syngas) production and for phosphorus recovery. In the first step, an anaerobic digestion (AD) process was carried out on two different mixtures of raw agro-industrial residues. Specifically, a mixture of asparagus and tomato wastes (mixture-1) and a mixture of potatoes and kiwifruit residues (mixture-2) were investigated. The results proved that the properties of mixtures notably affect the evolution of the digestion process. Indeed, despite the lower organic load, the maximum biogas yield, of about 0.44 L/gCODremoved, was obtained for mixture-1. For mixture-2, the digestion process was hindered by the accumulation of acidity due to the lack of alkalinity in respect to the amount of volatile fatty acids. In the second step, the digestates from AD were utilized for syngas production using supercritical water gasification (SCWG) at 450 °C and 250 bar. Both the digestates were rapidly converted into syngas, which was mainly composed of H2, CO2, CH4, and CO. The maximum values of global gasification efficiency, equal to 56.5 g/kgCOD, and gas yield, equal to 1.8 mol/kgTS, were detected for mixture-2. The last step of the integrated treatment aimed to recover the phosphorus content, in the form of MgKPO4ˑ6H2O, from the residual liquid fraction of SCWG. The experimental results proved that at pH = 10 and Mg/P = 1 it is possible to obtain almost complete phosphorus removal. Moreover, by using the scanning electronic microscopy, it was demonstrated that the produced precipitate was effectively composed of magnesium potassium phosphate crystals.